In general, the present invention relates to an air-bag control apparatus provided for controlling an air-bag unit. More particularly, the present invention relates to an air-bag control apparatus that is hardly affected by noise introduced onto a line transmitting a signal the driving air-bag unit, thereby being capable of avoiding a malfunction of the air-bag unit. Description of the Related Art
In recent years, there are an increasing number of cars in each of which an air-bag unit is provided on a steering wheel to protect the passengers against a shock caused by a car collision in the event of an accident.
FIG. 7 is an explanatory diagram showing the configuration of an embodiment implementing the conventional air-bag control apparatus. As shown in the figure, on the column side, there are provided an air-bag sensor 61 for detecting a collision of the car, a carrier generation means 62 for generating a carrier, a modulation circuit 63 for modulating the carrier and a transmission circuit 64 for transmitting a modulated carrier to the steering-wheel side. On the steering-wheel side, on the other hand, there are provided a reception circuit 65, a demodulation circuit 66 and an air-bag driving control circuit 67.
Next, the operation of the embodiment implementing the conventional air-bag control apparatus is explained by referring to FIGS. 7 and 8. The carrier generation means 62 on the column side generates typically a sinusoidal carrier like one shown in diagram A of FIG. 8 at normal times. This carrier is supplied to the modulation circuit 63 which is typically a balanced modulation circuit. At normal times, however, the modulation circuit 63 does not output a modulated carrier. Only when a modulation signal is supplied to the modulation circuit 63 does the modulation circuit 63 output a modulated carrier. Assume that the air-bag sensor 61 detects a car collision at a point of time t0. In this case, the air-bag sensor 61 generates a predetermined voltage E as shown in diagram B of FIG. 8. The voltage E serves as a modulation signal supplied to the modulation circuit 63. As a result, the modulation circuit 63 modulates the carrier supplied thereto by the carrier generation circuit 62 starting from the point of time to as shown in diagram C of FIG. 8 and outputs a modulated carrier to the transmission circuit 64. The transmission circuit 64 transmits the modulated carrier received from the modulation circuit 63 to the reception circuit 65. A signal is transmitted from the transmission circuit 64 to the reception circuit 65 through typically a non-contact coupling means (or a non-contact coupler not shown in the figure). The reception circuit 65 passes on the modulated carrier received from the transmission circuit 64 to the demodulation circuit 66. The demodulation circuit 66 demodulates the modulated carrier received from the reception circuit 65 to produce a predetermined voltage Exe2x80x2 shown in diagram D of FIG. 8 as a demodulated signal which is supplied to the air-bag driving control circuit 67. The air-bag driving control circuit 67 drives the air-bag unit in accordance with the demodulated signal.
Additionally, in recent years, there are many other pieces of electronic equipment installed in a car. The other electronic equipment generate and radiate a variety of electromagnetic waves and. An electromagnetic wave generated by the other electronic equipment may be introduced onto a transmission line between, for example, the modulation circuit 63 and the demodulation circuit 66 in the configuration of the conventional embodiment in spite of the fact that the car does not collide with anything and, hence, the air-bag sensor 61 does not generate the predetermined voltage E. When such an electromagnetic wave is introduced onto the transmission line, a noise signal like one shown in diagram E of FIG. 8 is supplied to the demodulation circuit 66 which then demodulates to inadvertently generate a demodulated signal like one shown in diagram F of FIG. 8. The demodulated signal is supplied to the air-bag driving control circuit 67. When this happens, the air-bag driving control circuit 67 inadvertently drives the air-bag unit in accordance with the demodulated signal generated by the demodulation circuit 66 in spite of the fact that the demodulated signal originates from an introduced noise signal.
When the air-bag unit is driven in spite of the fact that no accident such as a car collision takes place, the driver""s field of vision is blocked and driving is disturbed.
It is thus an object of the present invention to avoid a malfunction of an air-bag unit caused by an electromagnetic wave generated by various kinds of electronic equipment.
According to a first aspect of the present invention, there is provided an air-bag control apparatus: wherein first modulation means modulates a first carrier in accordance with a signal having a predetermined pattern from signal generation means to generate a first modulated signal and supply it to first demodulation means when collision detection means detects a car collision; the first demodulation means demodulates the first modulated signal to produce a first demodulated signal and supply it to signal comparison means; and the signal comparison means outputs an activation signal for activating an air bag only if the first demodulated signal matches the signal having the predetermined pattern.
According to a second aspect of the present invention, there is provided an air-bag control apparatus as in the first aspect, wherein the signal generation means comprises a plurality of switches for controlling car electronic equipment and a signal generation circuit for generating the signal having the predetermined pattern in accordance with an operating state of the switches.
According to a third aspect of the present invention, there is provided an air-bag control apparatus as in the second aspect, wherein the switches are installed on a steering wheel.
According to a fourth aspect of the present invention, there is provided an air-bag control apparatus as in the first, second or third aspect, wherein, the second modulation means modulates the second carrier in accordance with the signal having the predetermined pattern output from signal generation means to generate a second modulated signal and supply it to the second demodulation means; the second demodulation means demodulates the second modulated signal to produce a second signal; and the first modulation means modulates the first carrier in accordance with the second signal.
According to a fifth aspect of the present invention, there is provided an air-bag control apparatus as in the first aspect, wherein the signal generation means comprises a data retention unit for storing data having a predetermined format and a microcomputer, and the microcomputer reads out the data and generates the signal having the predetermined pattern.
According to a sixth aspect of the present invention, there is provided an air-bag control apparatus as in the fifth aspect, wherein two data retention units and two microcomputers are provided, and one of the data retention units and one of the microcomputers are provided on a column side, and one of the data retention units and one of the microcomputers are provided on a steering-wheel side.